Typically, a “plastisol” means a liquid polymer composition comprising a particulate form of at least one non-crosslinked organic polymer dispersed in a liquid phase comprising a plasticizer for the polymer. Plastisols also include “organisols”, which are plastisols in which solvents, such as liquid hydrocarbons, ketones, or other organic liquids, are used in amounts greater than about 5 wt. %, in addition to plasticizers, to control viscosity and other properties of the plastisol. Plastisols are used in a variety of applications, including without limitation flooring, screen inks, films, coatings, and molding and casting compounds.
Plastisols, by definition, are dispersions of polyvinyl chloride (PVC) and PVC copolymers. Acrylic-based plastisols are also common.
There are a large variety of plasticizers that have found use in plastisols. A typical plasticizer is defined as an organic liquid that will soften a polymer and make it more workable, as long as the polymer and plasticizer are at least partially compatible. Plasticizers are used to adjust hardness (or softness) of a polymer, impart stain resistance, alter tensile properties (such as strength, elongation or flexibility) and facilitate processability, as required, for a multitude of applications, including without limitation flexible vinyl applications. Plasticizers also serve as a vehicle for the dispersion of resin (polymer) particles, such as PVC.
Plasticizers are available in a wide variety of alternative chemistries and include: 1) general purpose, 2) specialty types and 3) secondary and diluent types, more fully described herein. A key distinction between plasticizers is their ability to solvate dispersed solid polymers and/or their gelation and fusion temperatures in plastisols. Gelation and fusion temperatures dictate the speed of production and are influenced by the solvating power of the plasticizer. By way of example only, the gelation and fusion temperatures of a plastisol containing a dibenzoate plasticizer will be lower than a plastisol containing a general purpose plasticizer, thus enabling speed of processing in that particular application.
General purpose plasticizers provide an excellent compromise between performance characteristics and economy for most applications. Some examples include: bis (2-ethylhexyl phthalate) (DEHP or DOP), diisononyl phthalate (DINP), dioctyl phthalate (DnOP), diisodecyl phthalate (DIDP), dipropylheptyl phthalate (DPHP), di-2-ethylhexyl terephthalate (DOTP or DEHT), and diisononyl-1,2 cyclohexane dicarboxylate (DIDC, or BASF's Hexamoll™ DINCH®).
Specialty type plasticizers were developed, in part, to fulfill the need for high solvators, the most popular historically being lower molecular weight phthalates. Examples include butyl benzyl phthalate (BBP), di-n-butyl phthalate (DBP) and diisobutyl phthalate (DIBP). Examples of non-phthalate, high solvating plasticizers include benzoate esters, some citric acid esters, alkyl sulfonic acid esters, and certain phosphates. Dibutyl terephthalate (DBTP) and n-alkyl pyrrolidones have also been proposed as specialty type, high solvating plasticizers.
Benzoate ester plasticizers include dibenzoates and monobenzoates. Useful dibenzoates include diethylene glycol dibenzoate (DEGDB), dipropylene glycol dibenzoate (DPGDB), triethylene glycol dibenzoate (TEGDB), 1,2-propylene glycol dibenzoate (PGDB), and blends thereof. Monobenzoate esters known to be useful as plasticizers include: isodecyl benzoate, isononyl benzoate, and 2-ethylhexyl benzoate. Benzoate ester plasticizers, alone and in combination, have a broad range of compatibilities with polymers utilized in the plastisol industry and possess good solvating and rheology characteristics that compare favorably to traditional high solvating phthalates.
Examples of secondary and diluent type plasticizers, used primarily to reduce plastisol viscosity, include those based on castor oil and soybean oil. Isodecyl benzoate, a monobenzoate, is also a useful diluent type plasticizer.
All of the high solvator plasticizers discussed above (regardless of type) add value to vinyl compositions that traditional general purpose plasticizers cannot. Traditional general purpose plasticizers have good rheology profiles, but have poor solvating ability.
While solvating characteristics are important, most high solvating plasticizers are limited in their usefulness due to high plastisol viscosity or poor plastisol rheology characteristics. An ideal plasticizer possesses a good balance between the solvation and rheology characteristics they impart. In many applications, particularly plastisols, high solvating plasticizers require the use of organic solvents to reduce viscosity for processability. Useful solvents include liquid hydrocarbons, ketones, and other organic liquids. An example of a useful solvent is Santicizer® 375, a mixture of C10-C16 alkyl benzenes and normal low molecular weight paraffins (˜20%).
The use of diluents to minimize the viscosity of a plastisol is known in the art. U.S. Pat. No. 8,034,860 to Arendt et al. describes a plastisol comprising an organic polymer, a plasticizer and an organic liquid and a method for preparing the plastisol that predictably yields low viscosity. Arendt et al. describe past trial and error practices of selecting suitable diluent/plasticizer combinations to maintain low viscosity. Arendt et al. discovered that when replacing a phthalate (BBP) plasticizer with the dibenzoates of DEG and DPG, a 25-fold increase in plastisol viscosity resulted, which was too viscous for processing. The viscosity could not be reduced to a processable level using a common liquid hydrocarbon mixture (63 wt. % aromatic hydrocarbons, 15 wt. % mixed aliphatic hydrocarbons and 22 wt. % normal paraffinic hydrocarbons) traditionally used with plastisols that contain BBP as the plasticizer. Arendt et al. resolved the problem by using an additional solvent that would meet a specified Hildebrand solubility relationship.
In particular, Arendt et al. discovered that the viscosity of a plastisol is directly related to a previously unknown mathematical relationship between the Hildebrand solubility parameter of the polymer and the weight average of the Hildebrand solubility parameters of the organic diluent(s), plasticizer and any other liquid ingredients present in the plastisol. The solution to the problem of higher viscosity was resolved by Arendt et al. by selecting solvent components based upon their Hildebrand solubility parameters. Specifically, selection of a proper type and amount of diluent (solvent) uses a mathematical relationship between: a) the Hildebrand solubility parameter of the polymer portion and b) a weighted average of the Hildebrand solubility parameter values of all liquid ingredients of the plastisol. The differences between a) and b) must be within specified limits (±0.6 to about ±1.0) to minimize plastisol viscosity and/or avoid the possibility of exudation of liquids from articles formed by the plastisol.
Compatibility between the polymer and plasticizer are important to performance of the plastisol. For the plasticizer to function, it must be at least partially compatible with the polymer. Use of solvents to minimize viscosity may result in incompatibility as well, when the primary plasticizer is not compatible with the solvent.
A novel method for minimizing the viscosity of a plastisol, while maintaining compatibility among the components, has been developed that does not require adjusting the solubility parameters of the plastisol components, in particular the solvents, to accommodate the plasticizer, nor selecting solvents purely on the basis of solubility parameters. Rather, the novel method adjusts the plasticizer composition to accommodate the traditional solvents used in plastisols, but does not require maintaining strict limits for the difference (±0.6-±1) between the Hildebrand solubility parameters of the dispersed polymer and that of the liquid phase components. In particular, it has been discovered that dibenzoate blends of plasticizers can be modified using either PGDB or dioctyl succinate (DOSx) to change their solubility parameters sufficiently to achieve compatibility with hydrocarbon liquid mixtures (solvents) traditionally used in plastisols. DOSx has not heretofore been used in the flooring industry. The inventive method has particular utility in the flooring industry, but the invention is not limited as such. The method may be utilized with plastisols for a variety of applications.
The method utilizes a novel plasticizer blend that does not require any alteration in the selected organic solvent. The blend comprises, in one embodiment, a compatibilizing plasticizer component, dioctyl succinate, which is completely compatible with high solvating plasticizers, such as the benzoate esters, and renders the benzoate plasticizer compatible with the organic solvent. In other embodiments, the novel blend comprises 1,2-propylene glycol dibenzoate (PGDB), 3-phenyl propyl benzoate (3-PPB), or other compatibilizing plasticizer components, all of which are also completely compatible with high solvating benzoate ester plasticizers, in amounts sufficient to render the benzoate ester plasticizers compatible with the organic solvent.
The novel methodology and blend(s) are based upon the changing of the polarity of the plasticizer system, which results in unexpectedly reduced viscosity of the plastisol, even in systems where components have previously been regarded as incompatible. The novel blend results in better viscosity and fusion points through the addition of a plasticizer component. The novel method does not require changing the organic solvents traditionally used in plastisols.
It is an object of the invention to provide a novel plasticizer blend for use in plastisols, which is compatible with a wide variety of organic solvents.
It is a further object of the invention to provide a plastisol composition comprising the novel plasticizer blend.
It is yet another object of the invention to provide a method of maintaining compatibility between a plasticizer(s) and an organic diluent in a plastisol composition.
Still a further object of the invention is to provide a liquid phase in which to disperse a polymer, comprising a plasticizer(s) and an organic diluent, wherein the plasticizer is completely compatible with the organic diluent mixture.